What is the test for having a valid signature on a document?

In response MCAP relies on the decision in Royal Bank v. McLean where the classic statement of the law can be found at para. 70: Whenever a man of full age and understanding, who can read and write, signs a legal document which is put before him for signature - by which I mean a document which, it is apparent on the face of it, is intended to have legal consequences - then, if he does not take the trouble to read it, but signs it as it is, relying on the word of another as to its character or contents or effect, he cannot be heard to say that it is not his document....he cannot go back on it, and say it was a nullity from the beginning.